This disclosure relates to an anti-extrusion seal assembly, and more particularly to such an assembly utilizing a backup ring and flange wedge assembly.
In a seal assembly for mating metal surfaces, for example where a shaft penetrates a pressure vessel, backup rings are installed on the low pressure side of an o-ring to help prevent leakage of a fluid. An o-ring functions as a seal through the mechanical deformation of an elastomeric compound. If the o-ring cannot resist increasingly higher pressures or if clearances in the seal assembly are too great, the o-ring may extrude into the clearances in the seal assembly. Backup rings are used to block the clearances and to provide axial support for the o-ring. Materials ""such as leather, polytetraflouroethylene (PTFE, TEFLON(copyright)), nylon or other similar materials are used on anti-extrusion devices. However, these devices must be manufactured dimensionally to meet radial clearances required to prevent seal extrusion while under operating pressures.
Thus, it would be advantageous to provide an anti-extrusion seal assembly where the components thereof can be manufactured with wider radial tolerances while not compromising ability of the seal assembly to prevent ""seal extrusion or where large insertion forces or interference conditions are not needed, facilitating installation and minimizing the resulting component eccentricity.
A seal assembly for a shaft is disclosed. The seal assembly comprises a flange fixed to a work piece having a bore hole therein. The bore hole is receptive of the shaft. The flange encircles the shaft and includes a generally triangular shaped projecting member having a first surface extending from the flange into the bore hole parallel to the centerline thereof and in contact with an inner surface of the bore hole. A second surface extends from the flange into the bore hole at an angle to the centerline thereof and joins the first surface. The flange also includes a landing surface perpendicular to the centerline of the borehole. The triangular shaped projecting member defines an annular space between the shaft, the landing surface and the second surface of the triangular shaped projecting member. A backup ring encircles the shaft and is positioned within the space defined between the shaft, the landing surface and the second surface of the triangular shaped projecting member. The backup ring makes contact with the second surface of the triangular shaped projecting member. The backup ring has a trapezoidal cross section which includes a flat third surface parallel to the landing surface, an opposing concaved fourth surface having a curvature directed away from the third surface and an angled fifth surface contiguous, and in slidable contact, with the second surface.
A first variable clearance is defined between an inner surface of the backup ring and an outer surface of the shaft or the surface of the bore hole. A second variable clearance is defined between the third surface of the backup ring and the landing surface of the flange. An o-ring encircles the shaft so as to be in physical contact with the shaft, the backup ring and the bore hole and is positioned Within the curvature of the concaved surface.